Forum: NGINX Why Nginx Doesn't Implement FastCGI Multiplexing?

Hi,

I'm doing some research on FastCGI recently. As I see from the FastCGI
specification, it does support multiplexing through a single
connection. But apparently none of the current web servers, like
Nginx, Apache, or Lighttpd supports this feature.

I found a thread from nginx dev mailing list back to 2009, stating
that multiplexing won't make much difference in performance:
http://forum.nginx.org/read.php?29,30275,30312

But I also find an interesting article on how great this feature is,
back to 2002:
http://www.nongnu.org/fastcgi/#multiplexing

I don't have the ability to perform a test on this, but another
protocol, SPDY, that recently becomes very popular, and its Nginx
patch is already usable, also features multiplexing. So I'm curious
about why spdy's multiplexing is great while fastcgi's is not.

One reason I can think of is that tcp connection on the internet is
expensive, affecting by RTT, CWND, and other tube warming-up issue.
But tcp conneciton within IDC (or unix-domain socket on localhost) is
much cheaper. Besides, the application can also go the event-based
way, to accept as much connections as it can from the listening socket
and perform asynchronously.

Does my point make sense? or some other more substantial reasons?

Thanks

Jerry

Hello!

On Sat, Mar 09, 2013 at 10:43:47PM +0800, Ji Zhang wrote:

>
> But I also find an interesting article on how great this feature is,
> back to 2002:
> http://www.nongnu.org/fastcgi/#multiplexing

This article seems to confuse FastCGI multiplexing with
event-based programming.  Handling multiple requests in a single
process is great - and nginx does so.  But you don't need FastCGI
multiplexing to do it.

> and perform asynchronously.
>
> Does my point make sense? or some other more substantial reasons?

You are correct, since FastCGI is used mostly for local
communication, multiplexing on application level isn't expected to
be beneficial.  Another reason is that multiplexing isn't
supported (and probably will never be) by the major FastCGI
application - PHP.

There were several discussions on FastCGI multiplexing here, and
general consensus seems to be that FastCGI multiplexing might
be useful to reduce costs of multiple long-polling connections to
an application, as it will reduce number of sockets OS will have
to maintain.  It's yet to be demonstrated though.

--
Maxim Dounin
http://nginx.org/en/donation.html